We can agree that we will not agree all the time. If you grasp that concept—and are okay with it—congratulations, that is all you need to manage when it comes to expectations. In fact, that should be your end goal when going into arguments with family and friends. If both arguing parties can agree to disagree, it is a major win.
Do not count on agreeing to disagree with your family though. Emotions run deep; the risks are high. Remember, you cannot “unfamily” them. Nor should you. My advice here, if you cannot be civil, avoid any moral or political discussions (since they seem to be the same). You may only speak about the weather, which cannot be influenced or corrupted.
If things go south, request a cease-fire, and if that does not work, it may be best to leave or ask them to leave. Love them – for they are partisan to just one side of the coin. Resistance is futile.